In this chapter, we discuss the algebra framework that guides our work and how this framework was enacted in the design of a curricular approach for systematically developing elementary-aged students' algebraic thinking. We provide evidence that, using this approach, students in elementary grades can engage in sophisticated practices of algebraic thinking based on generalizing, representing, justifying, and reasoning with mathematical structure and relationships. Moreover, they can engage in these practices across a broad set of content areas involving generalized arithmetic; concepts associated with equivalence, expressions, equations, and inequalities; and functional thinking. [This paper was published in: C. Kieran (Ed.) "Teaching and Learning Algebraic Thinking with 5- to 12-Year-Olds: The Global Evolution of an Emerging Field of Research and Practice" (p27-49). Hamburg, Germany: Springer International.]